This invention relates to lubricated aluminum weld wire, or metallizing wire, with a nascent aluminum surface, for use in a continuously fed welding machine, or metallizing means, respectively; and, a process for spooling an arbitrary length of such weld wire (so referred to herein irrespective of its use) in level layers on a spool which is hermetically sealed in an atmosphere containing a sufficiently high partial pressure of an essentially anhydrous lower alkanol, high enough to provide protection to the weld wire. This invention also relates to a process for welding with the weld wire to form a weld bead essentially free of pores and occluded hydrogen; and, to a process for metallizing with the weld wire to deposit aluminum vapor essentially free of pores and occluded hydrogen. In each case, the weld wire is typically fed off the spool through guides in the feeding means of the continuous welding or metallizing means, respectively.
By "nascent aluminum" (sometimes referred to as "ultraclean" weld wire, though not all ultraclean weld wire has a nascent aluminum surface) I refer to aluminum alloy which is essentially free of aluminum oxide. Because my weld wire is coated with lubricant, it is not ultraclean; therefore, reference to ultraclean weld wire herein, refers to nascent aluminum weld wire which is essentially free from lubricant or solvent. By "aluminum weld wire" I refer to flux-free solid wire, less than 0.25 inch (about 7 mm) thick, of an aluminum alloy which is predominantly aluminum. Fluxed aluminum welding wire is of no interest in this invention is fluxed weld wire introduces too many impurities. Hereafter, the term "weld wire" (for brevity) refers to "aluminum alloy weld wire" unless indicated otherwise. By "lubricated" I refer to the weld wire which is coated with dual thin layer, the first thin layer consisting of subtantially oil-free solid lubricant adherently deposited on the wire's surface, and the second thin layer consisting essentially of an anhydrous lower primary alkanol (hence, "dual-coated"). The solid lubricant is preferably essentially oil-free colloidal graphite ("ofc-graphite" for brevity), or, a mixture of essentially ofc-graphite and a colloidal sulfide of molybdenum, in which mixture the graphite is present in a major amount by weight.
Dual-coated weld wire is uniquely adapted to be fed, essentially continuously, without galling or binding in the guide means associated with power-feeding means of the welding machine. The dual-coated weld wire I make, is most particularly adapted to be so fed, after it is packaged by being wound in level layers of wire, one layer on top of the other, on a hermetically sealed cylindrical spool or reel to be mounted in an appropriate manner to allow the weld wire to be fed off the spool to the welding machine.
One skilled in the art will appreciate that aluminum alloy weld wire must be essentially free of contaminants which deleteriously affect the quality of the weld produced. Most common among such contaminants are the oxides of aluminum, which if present, produce a low quality, porous weld lacking requisite ductility.
Aluminum oxide contaminants are not present on weld wire which is freshly "shaved" or "stripped" in a shaving die, because the wire is protected with a protective layer of an inert relatively heavy lubricant oil which serves a dual purpose. The first is to lubricate the die while the nascent aluminum surface is exposed, for example, by drawing with a diamond die; and the second, is to protect the exposed nascent aluminum surface from oxidation in the ambient atmosphere.
Conventionally, oxided weld wire about 7 mm thick, is shaved in a flood of heavy mineral oil lubricant, or a water-soluble lubricant, then finished by drawing through a multi-die drawing means to the desired diameter (say, 0.062" or 0.3 mm), leaving a nascent aluminum surface coated with the heavy lubricating oil. This heavy lubricating oil is then washed off in a solvent bath, for example, 1,1,1-trichloroethane, and passed through a cocoon or swab of fiber placed at the outlet, to remove the solvent. The problem is that the swab is soon soaked with the oil, and unless the swab is replaced at frequent intervals, the surface of the weld wire becomes contaminated with the oil.
The benefit of such contamination is that the weld wire provides the lubricity required to "level-layer spool" the wire By "level-layer spooling" I refer to the wire being wound onto the spool in level layers, one on top of the other, each layer extending from one end-flange of the spool to the other. Thus each layer has the thickness approximating that of the diameter of the wire, and each layer lies in a circumferential annular zone having a depth, measured in the radial direction, about equivalent to the diameter of the wire.
The drawback of such contamination with the oil is that the weld produced with the easily spooled weld wire, is unacceptable. Of course, the frequency with which the swab is replaced can be minimized by having a large number of solvent baths in series, so that there is progressively less contamination of oil if each successive bath, the last bath being essentially pure solvent. Obviously, this is a less practical solution than replacing the swab frequently.
When a fresh swab is used, the weld wire is "ultraclean" and produces a high quality weld. The problem is that the weld wire has no lubricity. As a result, it resists being spooled in level layers, typically requiring a spooling guide means, often supplemented by manually, frequently guiding the wire with a stick, as the occasion and visual inspection demands, to level-layer wind the wire onto the spool. Overcoming the problem of spooling the ultraclean wire, in turn, begets the complementary problem of having the wire gall and bind in the feeding means to the welding gun, not too surprisingly, since the wire has no lubricity. It is well known that bare aluminum surfaces are not well adapted for use with other metal surfaces because of the inherent softness of the metal and its tendency to bind or adhere, especially when in contact with other bare aluminum surfaces. When the wire stops feeding, the welding stops until the feed is reinstated.
With respect to the problem of level-layer spooling, lubricating an aluminum surf-ace to be in contact with another metal or aluminum surface, was suggested by Work et al who used finely divided graphite secured to the bare aluminum base with an artifically produced aluminum oxide coating formed by aluminum and an alkali metal silicate, as more fully described in U.S. Pat. No. 2,157,155 (Cl. 91/subcl. 68). Clearly, they were aware of the difficulty of coating a bare aluminum surface with finely divided graphite without a binder. The problem was ameliorated when "colloidal-graphited water", a dispersion of colloidal graphite in water, was used, rather than in a non-aqueous and relatively non-volatile vehicle such as soils, greases and glycerin (see pg 2, col 1, lines 32-41).
Recognizing the desirability of having only graphite as the lubricant, and the attendant difficulty of adhering the graphite to any welding wire surface (since no particular metal is specified, presumably including aluminum, magnesium, tantalum, titanium, etc.) Kobayashi describes (in Japanese Patent No. 55-139,195 assigned to Matsuhita Electric Industries) a welding wire surface coated with an anti-corrosion substance, lubricant, etc., by rubbing the wire on the solid substance at an appropriate speed at either a perpendicular or inclined angle, the thrust of the invention being to control the amount of graphite adhering to the wire by varying the force with which the solid is pressed against the wire, and by changing the orientation of the solid so that it is worn more or less evenly, rather in a local `wear-spot`. Further recognizing that in many instances the presence of water may be detrimental to the quality of the weld produced with moisture contaminated wire, Kobayashi teaches heating the surface of the wire to a temperature in the range from above 100.degree. C. but below 250.degree. C. When welding wire is rubbed across a graphite block with sufficient force, such heating serves a two-fold purpose: it gets rid of moisture, and, it helps strip particles of graphite from the block. His invention teaches the criticality of not pressing the solid lubricant into the wire at a fixed position.
It is obvious in light of the all-encompassing scope of the disclosure, that if the anti-corrosion substance is lard, such rubbing against a lard block is unlikely to damage even magnesium wire, but that if the block is graphite, one would be forcefully ill-advised to rub the magnesium wire against the graphite block with susubstantial force and speed without expecting to damage the surface of the wire, or worse, cause a conflagration, especially if the magnesium wire was preheated. Knowing that Kobayashi's general disclosure is not applicable to all metal wire, one can only guess at what the effect of rubbing aluminum weld wire might be, particularly since one skilled in the art, by trial and error, would have to determine the force necessary, and the speed at which the wire is to be drawn across the block.
The necessary trial and error determination was made with aluminum weld wire having a nascent aluminum surface, and it was found that the surface of the weld wire is scored so severely as to interfere with mechanically feeding the wire to a continuous welding machine through guides in the feeding means Further, the graphite-coated wire so produced is of no interest for my intended purpose since it results in a wire coated with only graphite, and not a dual-coating. The demonstrative evidence provided by the appended photomicrographs provides a visual distinction between the spotted-graphite (so termed because of the separation of particles which provides a substantially monoparticulate thin layer) nascent aluminum surface of my dual-coated weld wire, and any prior art weld wire, particularly those produced by the techniques disclosed in Kobayashi.
To emphasize the criticality of the method of coating a wire with the expectation of obtaining a specifically characterized coating on it, Kobayashi deliberately recites what superficially appear to be comparably effective conventional techniques for coating welding wire, but are not equally effective. Such techniques are: (1) a final rolling using a liquid lubricant into which an appropriate amount of powdered graphite has been mixed, thus adhering the graphite to the wire surface; (2) passing the welding wire through a vessel containing powdered graphite, such that the graphite adheres to the wire surface; and, (3) coating the graphite by pressing it into wire at a fixed position. He specifically points out the deficiencies of techniques (1) and (2) namely, that the strength and adhesion of the graphite to the wire is low, and it is easy for the graphite to come off the wire surface during winding or other subsequent stages, and, it is difficult to control the amount of graphite which adheres to the wire.
In what appears to be an implicit reference to aluminum weld wire, he states, "In particular, technique (1), because it normally uses fats and oils such as paraffins, fatty acid esters, or mineral oils as lubricants, either singly or in combinations, is unusable for composite wire into which these fats and oils can easily penetrate, since the hydrogen emitted by these fats and oils will cause welding cracks and porosity in the weld." I nevertheless chose a hydrogen-containing dispersing medium, namely a lower alkanol having from 2 to 4 carbon atoms, as the continuous phase in my solid lubricant dispersion (in which the solid is the dispersed phase), but require that the alkanol be free from water in an amount sufficient to adversely affect the physical qualities of the weld made with the weld wire.
With particular respect to technique (2) Kobayashi states that "the graphite can build up in large quantities in some spots, so that this graphite piles up as it is scraped off the surface of the wire inside the wire feed path during welding; smooth welding is thus frequently interrupted; and, because powdered graphite is used as is, ease of handling is extremely poor."
Thus, the art recognizes that the method of coating welding wire generally, the particular lubricant used, and the specific form in which the lubricant is used, each produce a different coating on the wire. Moreover, it is obvious that adequately lubricated weld wire will level-layer spool. With specific respect to weld wire (with a nascent aluminum surface) it is also obvious that if the lubricant is thoroughly removed, it will produce a low porosity, high-quality weld of requisite ductility, inter alia. Since shaving the weld wire without a lubricant was not practical, the emphasis turned to feeding a lubricant-free weld wire to the welding gun with a simplified feeding means which would not bind the weld wire.
Though the ultimate problem to be solved was to produce high quality welds with continuously fed weld wire having a nascent aluminum surface, the immediate problem was to level-layer spool the wire so that it could be fed smoothly through the feeding means of a welding machine. For obvious reasons, the problem could not have arisen prior to the advent of `continuous-feed` welding machines for aluminum weld wire. Also for obvious reasons, the creation of a lubricated aluminum weld wire with known lubricants, for the sole purpose of lubricating it, is well within the skill of the art of lubricating wire for wire-feeding machines.
Thus, despite knowing that a lubricated weld wire was unsuitable for the intended purpose, I nevertheless chose to focus my efforts towards using a lubricated weld wire to produce a high quality weld. I therefore needed to direct my efforts to each step of producing a lubricated nascent weld wire in level-layers on a spool, then finding a lubricant, whether the safe or another, which did not interfere with producing the desired high quality weld. In addition, the surface of the weld wire had to be essentially free of hydrogen-containing contaminants, particularly moisture, or the quality of the weld is unacceptable. Solutions to the problem of providing aluminum weld wire free of deleterious contaminants are more fully described, for very different approaches to the problem, in U.S. Pat. Nos. 3,348,979 to Murphy et al (Cl. 148/subcl. 6.2) and 3,676,309 to Dolomont (Cl. 207/subcl. 27). By "essentially free of "moisture" I refer to the presence of less than 1000 ppm of water in the lubricant-coating, which in my invention, is the dual-layer coating.
I chose to retain the heavy mineral oil for the shaving dies, then aggressively clean off the weld wire coated with the mineral oil (referred to herein as the first lubricant) with a series of solvent rinses so that the weld wire is ultraclean (that is, having a nascent aluminum surface uncontaminated be any material), then replacing the first lubricant with a second, solid lubricant which would not interfere with the quality of the weld. In addition, the lubricated wire would need to be protected against oxidation after it was spooled, during the period it was shipped, stored and eventually used in a continuous welding machine.
Numerous references disclose lubricant compositions for aluminum, among these being U.S. Pat. Nos. 3,391,033 to Chevigny et al (Cl. 148/subcl. 6.27); and 3,895,971 to Bushey et al ,.Cl. 148/subcl. 6.27), inter alia. None suggests the combination of an anhydrous lower alkanol in combination with colloidal graphite, which is the subject matter of my U S. Pat. No. 4,674,672 (Cl. 228/subcl. 135), or, a major amount by weight of colloidal graphite and a minor amount of a molybdenum sulfide.